The invention relates to rotational mold apparatus and, more particularly, to rotational mold apparatus for melting a slush casting material on a heated mold to form a gel layer thereon which is subsequently cured by passage through a curing oven.
Various proposals have been suggested for directing liquid slush casting plastisol or dry powder slush casting material onto heated mold surfaces for forming a gel layer thereon of plastisol. Excess material is removed from the mold by extracting excess material therefrom either by pumping or dumping the excess material out of the mold and thereafter the gelled layer is subsequently cured.
An example of such a system is set forth in U.S. Pat. No. 4,389,177 wherein selective areas of a heated slush casting mold are maintained at different temperatures to control the rate of buildup of the gelled layer on the part. The '177 patent discloses a single mold, modular slush molding machine for manufacturing individual ones of such instrument panels. The machine is not adaptable to processing of a series of molds on a high volume, continuous assembly line basis.
U.S. Pat. No. 4,690,626 discloses a rotational mold system having multiple stations for cooling molded parts following heating at a centrally located heat source. A plurality of mold supports are located around an outer circular conveyor line. The mold tools are moved along the outer circular conveyor path until they are aligned with one of a plurality of radially inwardly directed conveyor paths. Then the tools are conveyed to the heat sources. Thereafter they are moved along the same radial path into alignment with a mold cooling chamber.
The '626 patent does not provide a cure path for fusing gelled plastic material on the mold after the slush casting material (either liquid plastisol or dry) is cast onto the surface of a preheated mold assembly as discussed in the aforementioned U.S. Pat. No. 4,389,177.
U.S. Pat. Nos. 2,834,986 and 2,893,057 disclose rotational casting machines for casting vinyl resins onto the surface of hollow mold forms. The machines have a single circular conveyor path which is in part used to preheat molds which are then charged with slush casting material such as vinyl resin and thereafter rotated to distribute the vinyl resin material onto the inner surface of the mold. The charge of mold material is selected to produce a desired thickness layer of vinyl material on the mold. Following the formation of a gel layer, the mold is directed through a curing oven and a cooling oven both of which are located on the single circular conveyor path. The machines do not provide for drain of plastisol nor do they provide for the extended length cure path of the present invention.
U.S. Pat. No. 4,028,038 discloses a rotational molding machine having six mold carriers mounted at equidistant points around a horizontal axis of the machine. Two coaxial shafts are connected to first and second drive wheels one of which rotates the mold on its axis and the other of which drives the mold with respect to index positions of the machine. The machine has a single circular conveyor path. The machine does not provide the extended length curing path of the present invention.
U.S. Pat. No. 3,151,196 discloses a molding system having the steps of filling, gelling, dumping excess slush cast plastisol and heating to fuse the gelled material. Thereafter the part is cooled and stripped from the mold. All the process steps are accomplished on a single, large diameter, circumferentially formed conveyor path.
None of the aforesaid patents disclose a dual arm assembly on which two molds are simultaneously gelled and cured and wherein mold reversing means are provided to sequentially position one or the other of the two molds in a respective gel or cure conveyor path.